Methods of preparing a surface-activated titanium oxide product and of using same in water treatment processes

ABSTRACT

A method for removing dissolved contaminants from solution using a surface-activated crystalline titanium oxide product having a high adsorptive capacity and a high rate of adsorption with respect to dissolved contaminants, in particular, arsenate and arsenite. Preferably, the titanium oxide product includes crystalline anatase having primary crystallite diameters in the range of 1-30 nm. The surface-activated titanium oxide is combined with other filter media to further improve the removal of dissolved contaminants.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/304,550, filed on Nov. 26, 2002, now U.S. Pat. No.6,919,029, and which claims the benefit of U.S. Provisional PatentApplication No. 60/357,051, filed on Feb. 14, 2002.

FIELD OF INVENTION

The present invention relates to products and methods for removingdissolved contaminants from aqueous and organic streams. Moreparticularly, the present invention relates to methods of removingdissolved inorganic contaminants from aqueous streams using asurface-activated crystalline titanium oxide product as an adsorbent.The method is non-photocatalytic, and does not require irradiation forthe removal of contaminants. In addition, the present invention allowsremoval of inorganic contaminants in streams containing 50% (w/w) ormore of an organic material, such as ethylene glycol.

The method of the present invention makes use of adsorbent materialsdescribed in U.S.Pat. No. 6,919,029. The surface-activated crystallinetitanium oxide product of this invention can be in the form of a powder,or mixed with a binder to form an agglomerate or granule. Theagglomerate may be further processed by grinding, extruding, orcombining with other filter media. The surface-activated crystallinetitanium oxide product can also be incorporated into a paper or sheet.Such papers or sheets can be further processed into a pleated filter, aspiral wrapped filter, or a carbon block wrap layer.

BACKGROUND OF INVENTION

Wastewater and natural waters (e.g., surface water or groundwater) maycontain a variety of dissolved inorganic substances from natural andanthropogenic sources. Regulatory limits have been set for a number ofthese substances in drinking water and for discharges to natural waters,for protection of public health and of environmental quality. Theregulatory limits for many of these substances are set at very lowlevels, e.g., in the range of 2-50 parts-per-billion (“ppb”) or theequivalent units of measure of micrograms-per-liter (“μg/L”).

Conventional water treatment processes, such as co-precipitation withiron or aluminum salts, lime softening, or filtration using adsorbentsor ion exchange resins, are ineffective in removing some of theseregulated substances to the mandated levels. This problem is ofparticular concern with respect to certain types of substances includingoxyanions, particularly arsenate and arsenite, and some metals, such asmercury, because of their chemistry in water and the particularly lowregulatory limits that have been set for them. Typically, the removal ofsuch contaminants can be improved by selecting a treatment matrix (e.g.,a co-precipitant or adsorbent) that exhibits a greater capacity tosequester or retain the dissolved substance of concern, or provides morefavorable kinetics toward that substance (i.e., the treatment reactionproceeds more quickly). The low capacity or unfavorable kinetics of atreatment matrix can be accommodated to some extent by construction oflarger treatment systems to allow the use of larger quantities of thetreatment matrix or to provide longer contact times between thetreatment matrix and solution undergoing treatment. The costs ofbuilding and operating such a system increase with the size of thesystem and often cause such an accommodation to become uneconomical.

U.S. Pat. No. 6,383,395 discloses the use of powdered titaniumhydroxide, packed in a column or applied to a filter in the form of apaste, to remove dissolved oxyanions, particularly arsenate, from water.

U.S. Pat. No. 3,332,737 discloses the use of hydrous titanium oxides inpacked columns to adsorb several dissolved metals. The hydrous titaniumoxides are prepared by treating a solution of a hydrolysable titaniumcompound with aqueous ammonia or hydrogen peroxide.

Japanese Patent Application Publication 58-45705 discloses the use ofhydrous titanium oxides in slurries to remove oxyanions, such asarsenate, from water at concentrations in the parts-per-billion (ppb)range. The hydrous titanium oxide adsorbent is prepared from aprecipitate of a hydrolyzed titanium salt. Japanese Patent ApplicationPublication 58-45705 teaches that the kinetics of adsorption arerelatively slow, and that a contact time roughly five times as long isrequired to remove the same amount of arsenate from solution in theabsence of certain non-oxygenated acidic anions, such as chloride orsulfide, as when the acidic ions are present.

Japanese Patent Application Publication 53-122691 discloses thepreparation and use of a composite adsorbent comprising a granularactivated carbon and hydrous titanium oxides. The composite adsorbent isprepared by boiling the granular activated carbon in a concentratedsolution of a titanium salt in the presence of an oxidative acid, thenwashing and air-drying the resulting composite adsorbent.

Powdered agglomerate or granulate can be formed into various flat sheetsor composite filter media. Examples of flat sheets are taught, forexample, in U.S. Pat. No. 5,997,829; U.S. Pat. No. 6,719,869; or U.S.Pat. No. 6,797,167. A newer form of flat sheet is an integrated paperformed with nanofibers in a wet laid paper-making process, taught inU.S. Publication No. 2004/0178142 A2. The surface-activated titaniumoxide product of the present invention imparts improved heavy metalremoval over prior art titanium oxides.

SUMMARY OF THE INVENTION

This invention comprises a method for removing dissolved inorganiccontaminants from a solution using a surface-activated crystallinetitanium oxide product. A preferred embodiment uses surface-activatedcrystalline titanium oxide product made by preparing a titanium oxideprecipitate from a mixture comprising a hydrolysable titanium compoundand heating the titanium oxide precipitate at a selected temperature ofless than 300° C.; preferably, a temperature between about 100° C. and150° C.; or, more preferably, a temperature of about 105° C. Thepreferred method of preparing the surface-activated crystalline titaniumoxide precipitate does not include a calcining step.

In another preferred embodiment of the method, the surface-activatedcrystalline titanium oxide product is a nano-crystalline anatase. Thenano-crystalline anatase is a titanium oxide product having anatasecrystals with mean primary crystallite diameters within the range ofabout 1 nm to about 30 nm; preferably, within the range of about 1 nm toabout 10 nm. Dissolved inorganic contaminants to be removed from thedilute aqueous include antimony, arsenite, arsenate, cadmium, chromium,copper, lead, mercury, tungsten, uranium, and zinc, and low-molecularweight organic arsenic compounds, such as monomethylarsonic acid,dimethylarsinic acid, or phenylarsonic acid. The surface-activatedcrystalline titanium oxide product, preferably comprising anano-crystalline anatase, may be in a powdered form, in a granular formcomprising one or more binders, in the form of a coating on a substrate,or in other forms that will be obvious to those having ordinary skill inthe relevant arts.

Another aspect of the invention comprises a method for preparing apacked bed with surface-activated crystalline titanium oxide product toremove dissolved inorganic contaminants from a solution. The dilutedsteam is filtered through the bed and the surface-activated crystallinetitanium oxide product adsorbs the contaminants. A preferred form of thesurface-activated crystalline titanium oxide product is agglomerated orgranulated using a binder such as a thermoplastic polymer, athermosetting polymer, silicate, latex, or a polyvinyl acetate. The rateof removal of impurities for the preferred agglomerate or granulatesurface-activated crystalline titanium oxide product is improved overcomparable iron-based media.

Another aspect of the invention is the addition of the surface-activatedcrystalline titanium oxide product into other materials, devices, orforms, such as blocks, films, sheets, papers or honeycombs. Productsmade by such additions have been shown to be more effective in removingdissolved contaminants than the agglomerated or granulated adsorbentalone.

Another aspect of the invention is the use of surface-activatedcrystalline titanium oxide for removal of inorganic materials,especially heavy metals, from streams containing more than about 50% w/wof one or more organic compounds. The surface-activated crystallinetitanium oxide thus is useful for cleaning glycol coolants or industrialwaste streams.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the changes in influent and effluentconcentrations of arsenic over the number of bed volumes of an aqueousstream filtered through a packed column of nano-crystalline anataseprepared according to the present invention.

FIG. 2 is a bar chart of the efficiency of different forms of titaniumoxide, including a nano-crystalline anatase prepared according to thepresent invention, in removing dissolved arsenate from water.

FIG. 3 is a bar chart comparing the efficiency of anatase havingdifferent primary crystallite diameters in removing dissolved arsenatefrom water.

FIG. 4 is a bar chart comparing the crystallite diameters of samples ofanatase and the efficiency of the anatase samples in removing arsenatefrom water to the temperature at which the anatase is dried during itsproduction according to a method of the present invention.

FIG. 5 is a graph of an adsorption isotherm of arsenate (As (V))adsorption from water by nano-crystalline anatase prepared according tothe present invention.

FIG. 6 is a graph showing the effect of borate and phosphate on thearsenite adsorption capacity of granulated titanium oxide in an organicsolution containing 50% ethylene glycol.

FIG. 7 is a graph showing the effect of borate and phosphate on thearsenate adsorption capacity of granulated titanium oxide in an organicsolution containing 50% ethylene glycol.

FIG. 8 is a graph showing the effect of pH on the capacity of arsenicadsorption by granulated surface treated titanium oxide product in awaste ethylene glycol engine coolant.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises methods for producing surface-activatedcrystalline titanium oxide products, and methods for using such productsto remove dissolved inorganic substances from water. The term“surface-activated” refers to the high adsorptive capacities andfavorable adsorption kinetics of the titanium oxide products, which leadto high rates of removal for dissolved arsenate, arsenite, low-molecularweight organic arsenic compounds, metals such as lead, and otherdissolved inorganic substances. The “titanium oxide” of the presentinvention may be primarily, comprised of titanium dioxide; however,hydrous titanium oxide or other titanium oxides and hydroxides may bepresent in the product.

The primary commercial use of titanium dioxide is as a white pigment ina wide range of products. The pigments generally contain one of the twoprimary crystalline forms of titanium dioxide, anatase and rutile. Bothof these forms have the chemical composition TiO₂, but have differentcrystalline structures. Industrial processes that produce anatase andrutile typically use a sulfate process. A chloride process is also usedfor commercial production of rutile. Although it is not impossible toobtain anatase by a chloride process, the thermodynamics of the processmake it significantly more applicable to the production of rutile.

Additional uses of hydrous titanium oxides include photocatalyticprocesses, including removal of contaminants by photocatalysis, whereinthe photcatalyst is irradiated. The process of the present inventiondoes not require irradiation for removal of metals such as arsenic andlead.

Preferred surface-activated titanium oxide products and a method formaking them are described in U.S. Pat. No. 6,919,029. In the method, asurface-activated crystalline titanium oxide product is produced fromthe hydrolysis of a hydrolysable titanium compound such as titaniumsulfate, followed by precipitation of the resulting titanium oxide. Theconditions of precipitation are controlled so that the precipitate canbe easily filtered and washed, to produce crystals having the desiredcrystal structure and crystallite size. The washing step removes solublemetal salts that may remain in the product and reduces any acid content(e.g., sulfuric acid) of the resulting slurry.

The titanium oxide slurry from the separation and washing steps istreated with a neutralizing agent such as sodium hydroxide to adjust itspH toward 7. The neutralized titanium oxide contains salts, typicallysulfates, which fill a portion of the pore space of the titanium oxidesolids, but which may be removed by washing the solids with water orwith a dilute acid to improve the adsorptive properties of thesurface-activated crystalline titanium oxide product. The solids arethen dried under air or steam at a selected temperature between about50° C. and about 300° C. The drying temperature is selected to produce aproduct containing titanium oxide crystals having a desirablecrystallite diameter and surface activity, which may be expressed as thenumber of available surface hydroxyl groups per mass of titanium oxide.Smaller crystallite diameters, preferably in the nano-crystallite rangeof 1-30 nm, or, more preferably, between about 1 nm and about 10 nm, areachieved at the lower drying temperatures. The selected dryingtemperatures are maintained for 2 hours or less, producing asurface-activated titanium oxide product comprising functionalnano-crystalline titanium oxide. The drying stage of the presentinvention differs from a calcination stage that is typically present inprocesses for producing titanium oxide catalysts or pigments. Thetemperature of the drying stage of the present invention is selected toremove free water from the product, while the temperature of the typicalcalcination stage is selected to drive off sulfur oxides and otherresidues that may be bound to the product. Drying the product attemperatures higher than 300° C. dramatically impairs the adsorptiveproperties of the surface-activated crystalline titanium oxide product.No calcination stage is present in the methods, disclosed herein, ofproducing surface-activated crystalline titanium oxide products.

In general, a surface-activated crystalline titanium oxide is producedby adding water to a hydrolysable titanium compound (e.g., to form anaqueous solution of the hydrolysable titanium compound) and maintainingthe resulting mixture at a temperature between about 50° C. and about180° C. for a period of about 2 hours or longer. A more preferredtemperature range is between about 80° C. and about 120° C. Theselection of an optimum temperature for hydrolysis within these rangesdepends on the hydrolysable titanium compound used as a startingmaterial and the desired crystallite diameter of the precipitate afterdrying. For example, a solution of titanium oxysulfate may be maintainedat a temperature between about 80° C. and about 110° C. to produce aprecipitate that has a crystallite diameter between about 6 nm and about8 nm after drying. Under some conditions, the titanium oxide willprecipitate in an amorphous form (e.g., as a gel) rather than in acrystalline form. The amorphous product may be dried to form thesurface-activated crystalline titanium oxide and washed subsequently, ifdesired.

Other surface-activated crystalline titanium oxide products also may beproduced in accordance with the present invention. For example, aparticulate substrate, such as granular activated carbon or alumina, maybe coated with a surface-activated crystalline titanium oxide bycontacting the particulate substrate with the mixture of thehydrolysable titanium compound and water under controlled conditions toprecipitate the titanium oxide onto the surface or into the pores of theparticulate substrate. For another example, the dried surface-activatedcrystalline titanium oxide product may be powdered, and the powderreconstituted in a granular form with one or more binders. Thisreconstitution would facilitate the formation of granules havingselected adsorptive and/or structural properties. Preferred binders forthe surface-activated crystalline titanium oxides of the presentinvention include silicates, cellulosic polymers, vinyl polymers,thermoplastic binders, thermoset binders, and water. More preferredbinders include latex, sodium silicate, hydroxyethyl cellulose,polyvinyl alcohol and polyvinyl acetate.

As disclosed in the Examples below, the surface-activated crystallinetitanium oxide product of the present invention has a high adsorptivecapacity and favorable adsorption kinetics for removing oxyanions, suchas arsenate and arsenite, dissolved metals, and some low-molecularweight organic compounds at low concentrations in water, whichproperties lead to high rates of removal for those substances. Thesurface-activated crystalline titanium oxide product may be used tosubstantially reduce the concentrations of such substances toconcentrations below a few micrograms-per-liter (μg/L). Substances whichmay be effectively adsorbed by a surface-activated crystalline titaniumoxide product include aluminum, antimony, arsenic(I), arsenic(V),barium, cadmium, cesium, chromium, cobalt, copper, gallium, gold, iron,lead, manganese, mercury, molybdenum, nickel, platinum, radium,selenium, silver, strontium, tellurium, tin, tungsten, uranium,vanadium, zinc, nitrite, phosphate, sulfite, sulfide, and low-molecularweight organic arsenic compounds, such as monomethylarsonic acid,dimethylarsinic acid and phenylarsonic acid. In particular, thesurface-activated crystalline titanium oxide product is effective inadsorbing arsenite (As(III)), arsenate (As(V)) and the dissolved metalsantimony, cadmium, chromium, copper, lead, mercury, tungsten, uraniumand zinc. The removal of arsenite does not depend on the arsenic beingin ionic form. The product of this invention adsorbs arsenite in a pHrange of about 1 to 9, where the arsenite is typically in a protonatednonionic form as H₃AsO₃. The ability to adsorb in a neutral aqueousstream in a pH range from about 6.5 to 8.5 is important in removingarsenite from drinking water. Arsenite removal is especially importantfor the purification of groundwater. Groundwater is herein defined aswater originating or derived from underground sources. Arsenic presentin this water is often in the arsenite form because it has not yet beenoxidized to the arsenate form.

The preferred methods of making surface-activated crystalline titaniumoxide consistently produce a product that consists predominantly, if notentirely, of anatase crystals having crystallite diameters in the rangeof about 1 to about 30 nm. For the purposes of reference and discussion,such titanium oxide products will be referred to hereinafter as“nano-crystalline anatase” products.

The nano-crystalline anatase product of this invention may beagglomerated with an inorganic binder, such as a silicate or a latexbinder. The agglomerated product can be then used in a filtration columnin a packed bed. A packed bed of the agglomerated product has improvedkinetics and lower pressure drop when used in a column than iron oxidebased media in deep beds. The size of agglomerated product can vary. Apreferred particle size for packed beds is specified as having greaterthan 90% of the agglomerate by weight retained in a 60 U.S. mesh (0.25mm) screen

The agglomerated product, or a finer sized granulate powder, may beadded to other materials or devices, including, but not limited, tocarbon block and flat sheets made from materials such as cellulosicpolymers, other polymers, or nanofibers. The addition of the titaniumoxide product of the present invention to such materials or devicesimproves their performance in removing heavy metals. When added tocarbon block filters, the surface-activated titanium oxide product hassuperior lead removal properties, in comparison to amorphous titaniumsilicate.

Powdered agglomerate or granulate nano-crystalline anatase can be formedinto various flat sheets or composite filter media. Examples of flatsheets are taught, for example, in U.S. Pat. No. 5,997,829; U.S. Pat.No. 6,719,869; or U.S. Pat. No. 6,797,167, the disclosures of which arehereby incorporated for reference. A newer form of flat sheet is anintegrated paper formed with nanofibers in a wet laid paper-makingprocess, taught in U.S. Publication No. 2004/0178142 A2, the disclosureof which is hereby incorporated by reference. The surface-activatedtitanium oxide product of the present invention imparts improved heavymetal removal over prior art titanium oxides, in addition to the featuretaught in U.S. Publication No. 2004/0178142 A2.

Dissolved inorganic substances may be removed from a solution bycontacting the solution with a surface-activated crystalline titaniumoxide product for a period of time. Preferably, the surface-activatedcrystalline titanium oxide product comprises a nano-crystalline anatase,which material is particularly effective in removing arsenic anddissolved metals from water, as disclosed in the Examples. Forconvenience, the following methods of removing dissolved inorganicsubstances from water are discussed with respect to the use ofnano-crystalline anatase. However, any surface-activated crystallinetitanium oxide product may be used according to the methods of thepresent invention.

A solution may be contacted with a nano-crystalline anatase product byknown water treatment processes, e.g., suspending a powderednano-crystalline anatase in a batch or a stream of contaminated waterfor a period of time, then separating the nano-crystalline anatasesolids from the water, or by filtering the solution through a bed orcolumn of the nano-crystalline anatase product. The nano-crystallineanatase product used in water treatment processes may be in a powderedor granular form; it may be dispersed in a bed of a particulatesubstrate; or it may adhere to the surface or be within the pores of aparticulate substrate such as granular activated carbon or porousalumina.

The hydrolysable titanium compounds preferred for use include thefollowing inorganic compounds: titanium trichloride, titaniumtetrachloride, titanyl sulfate, titanium sulfate, titanium oxysulfate,titanium iron sulfate solution, and titanium oxychloride. Titaniumalkoxides may also be used, such as, titanium ethoxide, titaniumethylhexoxide, titanium isobutoxide, titanium isopropoxide, titaniumisopropylate or titanium methoxide.

As demonstrated by the Examples provided, the surface-activatedcrystalline titanium oxide product of the present invention provides ahigh degree of removal for the dissolved inorganic substances tested. Inparticular, the product removes more than 95% of the metals tested fromdilute aqueous solutions. Moreover, the surface-activated crystallinetitanium oxide product exhibits a high adsorptive capacity and favorablekinetics of adsorption toward arsenate and arsenite in dilute aqueoussolutions, reducing the concentration of those substances by about 80%with contact times on the order of 1 to 2 minutes. The surface-activatedcrystalline titanium oxide product can be produced from an intermediateslurry that is routinely generated in commercial titanium oxideproduction. Alternatively, it may be produced from any of a number ofcommercially available titanium compounds.

The effectiveness of surface-activated crystalline titanium oxide, andspecifically nano-crystalline anatase, in removing arsenate, arseniteand other dissolved inorganic substances from water is an unexpectedresult in view of the conventional understanding that the adsorptioncapacity of a metal oxide is controlled by the availability of hydroxylgroups on the surface of the metal oxide product (see, e.g., U.S. Pat.No. 5,618,437, col. 4, lines 26-30, and U.S. Pat. No. 6,383,395, col. 7,lines 49-53). However, a hydrous or amorphous titanium hydroxide shouldhave a greater number of available hydroxyl groups than a crystallinetitanium oxide and, therefore, would be expected to exhibit a greateradsorptive capacity according to the conventional understanding.

Example 6 demonstrates that, contrary to this expectation, thenano-crystalline anatase of the present invention has a higheradsorptive capacity than the amorphous titanium oxides. Moreover, thefavorable adsorption kinetics of the titanium oxide products of thepresent invention are observed in the absence of acidic anions, such aschloride or sulfide, in contrast to expectations based on the disclosureof the Japanese Patent Application Publication 58-045705.

There are various ways to produce the surface-activated titanium oxideof the current invention. For instance, the product may be produced froma slurry of uncalcined titanium dioxide produced by a sulfate process,instead of by a chloride process. Moreover, the surface-activatedcrystalline titanium oxide product may contain various amounts ofnano-crystalline rutile. A surface-activated crystalline titanium oxideproduct may also be produced from hydrolysable titanium compounds otherthan those disclosed herein. The apparatus and methods of removingdissolved inorganic contaminants from water may be varied within therange of variations presently known in the art, e.g., by replacing thepacked bed filter with a fibrous filter or by contacting solution with afluidized bed, while using a nano-crystalline anatase or anothersurface-activated crystalline titanium oxide product therein. Theproducts, apparatus and methods may also be applied to the removal ofdissolved organic substances other than the organic-substituted arseniccompounds disclosed herein, including organic-substituted metalliccompounds, such as tetra-ethyl lead, and oxygenated organic compounds,such as methyl-t-butyl ether (MTBE). The product of the presentinvention has superior lead adsorption, when compared to amorphoustitanium silicate, which is used in several commercial filters

The high adsorptive capacity, rapid adsorptive kinetics, and lowpressure drop of agglomerated crystalline surface-activated titaniumoxide make it particularly useful for a number of applications. Forexample, home water purification devices benefit from compactness, longlife, and low pressure drop. Water purification devices in homeappliances such as refrigerators, dishwaters, and washing machines mustbe small in size to fit in available space in these appliances whilestill having adequate adsorption capacity to provide long life. Otherhome appliances such as faucet-mounted water purification devices andpour-through pitchers benefit from long lifetime, compact size, and lowpressure drop.

After adsorption of heavy metals such as arsenic, the surface activecrystalline titanium oxide product of the present invention may bedisposed of using solid waste handling techniques known in the art. Whentested with standard oxidative and reductive methods for leaching, theused product does not exceed standards for release of the arsenic forland disposal of wastes. Current standard tests for contaminantleachability include: The Toxic Characteristic Leaching Procedure (USEPAMethod 1311, Test Methods for Evaluating Solid Waste, Physical/ChemicalMethods, EPA Publication SW-846) and the Waste Extraction Test(California Code of Regulations, Title 22, Division 4.5, Chapter 11,Article 5, Appendix 11).

As an alternative to land disposal, the adsorbent of the presentinvention may be regenerated using processes already known in the art(e.g., regeneration using an alkaline solution). In an optimized system,one column volume of regenerant could regenerate a packed bed. However,it often will be preferable to dispose of used adsorptive media (e.g.,in a landfill), because of complexities associated with the regenerationprocess, issues related to disposal of contaminant-containing streamsresulting from the regeneration process, and process economies.

The surface activated crystalline titanium oxide of the presentinvention is capable of removing contaminants from streams that aresubstantially organic in composition. Disposal of waste ethylene glycolcoolant that may contain arsenic at concentrations of hundreds ofparts-per-million (ppm) or milligrams-per-liter (mg/L) has beenproblematic because of state and federal hazardous waste regulations.Removal of arsenic species by adsorption onto a solid support beforedisposal is an attractive solution to this problem and offers apotential new market for adsorption media. Agglomerated titanium oxidemedia is capable of removing arsenic from streams containing 50% or moreethylene glycol. In the examples below, surface-activated titanium oxidemedia was used to treat an ethylene glycol solution to decrease thearsenic concentration from 250 ppm to less than 10 ppm.

The following Examples are intended to aid in the understanding of themethods and products of the present invention and are not intended tolimit the scope or spirit of the invention in any way.

EXAMPLE 1 Preparation and Characterization of a Surface-ActivatedTitanium Oxide Product

A powdered surface-activated titanium oxide product was prepared from atitanium oxide intermediate obtained from a commercial sulfate processused primarily to produce titanium dioxide pigments. The titanium oxideintermediate was collected as an acidic slurry after a separation andwashing stage, but before a calcination stage. The pH of the slurry wasadjusted to a pH between 4 and 9 with sodium hydroxide, and the slurrywas filtered to collect the titanium oxide solids. The titanium oxidesolids were washed with water to remove salts, and then dried at aselected temperature between about 105° C. and about 300° C. for about 2hours. Samples of the dried titanium oxide product were powdered andsieved to obtain a 100-standard U.S. mesh fraction (i.e., a fractionhaving a mean particle diameter of about 150 μm).

Step-scanned X-ray powder diffraction data for the powdered samples werecollected using an X-ray diffractometer (trademark: Rigaku DXR-3000,Rigaku/MSC Corporation, The Woodlands, Tex.) using Bragg-Brentanogeometry, an iron (Fe) anode operating at 40 kV and 30 mA, and adiffracted beam graphite-monochromator. Measurements were taken using a1° divergence slit and a 0.15 mm receiving slit. FeKα radiation from theFe anode, i.e., radiation having a wavelength of 1.9373 Å, was used asthe X-ray source. Data were collected between 15°-65° of 2Θ (where 2Θrepresents two times the angle of Bragg diffraction) with a step size of0.05° and a count time of 5 seconds per step. Measurements made onsilicon powder (NBS 640, a=5.43088) were used to correct the 2Θ values.

The X-ray diffraction patterns obtained for the powdered samplesincluded the characteristic peaks of the X-ray diffraction pattern ofcrystalline titanium dioxide for the FeKα wavelength used. Thecharacteristic diffraction pattern of crystalline titanium dioxide is acombination of peaks having maxima at 25.29°±0.3°, 38.00°±0.3°,47.90°±0.3°, 55.77°±0.3° and 62.71°±0.3° of 2Θ, with the most intensepeak having its maximum at 25.29°±0.3° of 2Θ.

Crystalline interplanar distances (d) were calculated using Bragg's law:2 d sin Θ=n λ

where Θ is the angle of diffraction; n is an integer value; and λ is thewavelength of the X-ray source, in this case, λ=1.9373 Å. Anatasecrystals have interplanar distances (d) between 3.45 and 3.60 Å, incontrast, e.g., to rutile crystals which have interplanar distances (d)between 3.20 and 3.30 Å. The calculated interplanar distances (d) forthe powdered samples of the titanium oxide product were determined to bewithin the characteristic range for anatase.

Primary crystallite diameters (d₀) were calculated by the Scherrerequation:d ₀ =K λ/β cos Θ,

where K is a statistically determined pre-factor, in this case, K=0.89;λ is the wavelength of the X-ray source, in this case, λ=1.9373 Å; β isthe pure full width, expressed in radians, of the peak at 2Θ=25.29° athalf of its maximum intensity, in this case,β=((1.215°-0.15°)×π)/180°=0.0186 radians, where 1.215° is the observedpeak broadening, 0.15° is the strain and instrumental peak broadening,and π=3.14; and Θ is the Bragg angle of diffraction. The calculatedprimary crystallite diameters for the titanium oxide product obtained bythe Scherrer equation were in the range of about 6.6 nm to about 10.89nm for samples dried at temperatures between about 105° C. and about700° C.

The X-ray diffraction spectrograph and the calculated interplanardistances (d) and Scherrer primary crystallite diameters (d₀)demonstrate that the granular surface-activated titanium dioxide productformed by the method described above is primarily, if not entirely,comprised of nano-crystalline anatase.

EXAMPLE 2 Porosity and Surface Characteristics of Nano-CrystallineAnatase

A sample of powdered nano-crystalline anatase was prepared according tothe method of Example 1 and dried at a temperature of 105° C. The BETspecific surface area and the porosity of the sample were determined bya static volumetric gas adsorption technique. Measurements were takenusing a gas-absorption/desorption analyzer (trademark: ASAP 2010,Micromeritics, Norcross, Ga.). A sample tube containing the sample ofnano-crystalline anatase was cooled in liquid nitrogen and evacuated todegas the sample. Measured amounts of nitrogen gas were then introducedand the amount of nitrogen adsorbed by the nano-crystalline anatase wasdetermined at a series of defined pressures. The resulting data, i.e.,curves of the volume of nitrogen adsorbed vs. the relative nitrogenpressure, were reduced using the BET equation to determine the BETspecific surface area of the sample and using the BJH method todetermine pore size distribution. The sample of nano-crystalline anatasewas determined to have a BET specific surface area of about 330 m²/gmand a total pore volume of 0.42 cm³/gm for pores with diameters lessthan 0.63 μm.

The available surface hydroxyl content, i.e., the number of hydroxylgroups available for chemical reaction, was measured for two samples ofnano-crystalline anatase that had been dried at different temperatures.The samples were prepared according to the method of Example 1. Onesample was dried at a temperature of 105° C. and the other sample wasdried at a temperature of 350° C. The available hydroxyl content wasdetermined by suspending 10 gm of the sample into 200 mL of a 0.01 molarsodium chloride solution, using a continuous nitrogen purge. The pH ofthe suspension was adjusted to 5.5 and maintained at that level for 1hour by addition of sodium hydroxide and hydrochloric acid. Thesuspension was then titrated with 0.2 molar sodium hydroxide to a pH of12 over a period of three hours. A blank solution of 0.01 molar sodiumchloride was pH-adjusted and titrated by the same procedure. Theavailable surface hydroxyl content was calculated from the amount ofexcess sodium hydroxide consumed in titration of the suspension,relative to the amount consumed in titration of the blank. The availablesurface hydroxyl content of the sample dried at 105° C. was determinedto be about 1.1 mmol/gm of nano-crystalline anatase. The availablehydroxyl content of the sample dried at 350° C. was determined to beabout 0.4 mmol/gm of nano-crystalline anatase.

EXAMPLE 3 Batch Adsorption of Dissolved Metals from Aqueous Solutions

A powdered nano-crystalline anatase product was prepared according tothe method of Example 1 using a drying temperature of 105° C. Aqueoussamples of dissolved metals, or of the species containing arsenate (As(V)) and arsenite (As (III)), were prepared for testing by dissolvingsalts of the selected substances in tap water to the initialconcentrations shown in Table 1, and adjusting the samples to a neutralpH. Batch experiments were conducted by adding the nano-crystallineanatase product to each aqueous sample, to obtain the titanium oxidecontent shown in Table I, and suspending the nano-crystalline anataseproduct in the aqueous sample by mixing for about one hour. The resultsin Table I show that the nano-crystalline anatase product removes alarge percentage of each metal from the respective aqueous solutions ina relatively short time, i.e., one hour or less. The high degree ofarsenite (As (III)) removal is particularly noteworthy, sinceconventional adsorbents, such as alumina or ferric hydroxide, are knownto have much lower capacities for removal arsenite. Similar degrees ofremoval were demonstrated in subsequent tests performed on samples ofarsenate, arsenite and metal salts dissolved in deionized water. Thesetests demonstrated that presence of chloride, or other acidic anions, isunnecessary for achieving high rates of removal with thenano-crystalline anatase product of the present invention.

TABLE 1 Removal of Dissolved Contaminants by Powdered Nano-CrystallineAnatase As(V) As(III) Cd(II) Pb(II) U(VI) Hg(II) Cu(II) Cr(VI) Initial50 50 1.0 1.0 8.0 0.5 0.5 0.1 concentration (mg/L) Final 9.1 13.0 0.0240.018 0.08 0.026 0.005 0.003 concentration (mg/L) Percent 81.8 74.0 97.698.2 99.0 95.5 98.8 97.0 removal (%) Titanium oxide 1.0 1.0 1.0 1.0 1.01.0 1.0 0.5 content (g/L)

EXAMPLE 4 Column Filtration of Dissolved Contaminants from AqueousSolution

Samples of nano-crystalline anatase product were prepared according tothe method described in Example 1 using a drying temperature of 105° C.,and sieved to obtain a 20-50 standard U.S. mesh fraction (i.e.,particles having an average diameter of about 0.30 to 0.85 mm). Thenano-crystalline anatase product was packed in a 1-inch diameter columnto a bed depth of 6 inches. Arsenate and lead were added to tap water toobtain concentrations of 100 μg/L of As (V) and 100 μg/L of Pb (II),respectively, in separate tap water samples. Each tap water sample waspumped through the packed column at an empty bed contact time (EBCT) of36-90 seconds. Effluent concentrations of both As (V) and Pb (II) wereless than 3 μg/L. The attainment of such low effluent concentrations ata short EBCT indicates that adsorption of these contaminants at lowconcentrations occurs at a very rapid rate using the nano-crystallineanatase product of the present invention.

EXAMPLE 5 Arsenic Removal from Natural Groundwater

A packed column of nano-crystalline anatase product was prepared asdescribed in Example 4. Natural groundwater containing about 25 to 40μg/L arsenic was pumped through the column at an EBCT of about 100seconds. As shown in FIG. 1, arsenic concentrations in the treatedeffluent were less than 2 μg/L; with breakthrough occurring after morethan 30,000 bed volumes of the contaminated groundwater had beentreated.

EXAMPLE 6 Comparison of the Removal of Arsenate from Spiked Tap Water byDifferent Forms of Titanium Oxide

Rutile having a primary crystallite diameter (d₀) of about 130 nm wasobtained from a titanium oxide manufacturer. Nano-crystalline anatasehaving a primary crystallite diameter (d₀) of about 6.6 nm was preparedas described in Example 1, using a drying temperature of about 105° C.Two different amorphous titanium hydroxides were also prepared: one(“amorphous A”) by rapidly neutralizing a solution of acidic titanylsulfate; and the other (“amorphous B”) by slowly adding water to asolution of titanium (IV) isopropoxide in isopropanol to hydrolyze thetitanium isopropoxide. Arsenate (As (V)) was added to samples of tapwater to an initial concentration of about 50 mg/L. About 0.1 gm of eachsample of titanium oxide was added to 100 mL of the tap water sample ata neutral pH and suspended therein by mixing for about 1 hour. As shownin FIG. 2, the rutile sample was ineffective in removing dissolvedarsenate from the tap water sample. The amorphous A and amorphous Bsamples removed 28% and 55% of the dissolved arsenate, respectively. Thenano-crystalline anatase sample showed the greatest removal of dissolvedarsenate at about 76% removal.

EXAMPLE 7 Effect of Anatase Crystal Size on Removal of Arsenate fromWater

A number of batch adsorption tests were performed in which samples ofpowdered nano-crystalline anatase product having different primarycrystallite diameters (d₀) were used to remove arsenate from tap watersamples. The data from these tests were analyzed to correlate the degreeof arsenate removal with the primary crystallite diameter (d₀) of theanatase sample. As shown in FIG. 3, the degree of removal was highestfor samples of anatase having the smallest primary crystallite diameters(d₀=6.6 nm) and lowest for samples of anatase having the largest primarycrystallite diameters (d₀=134 nm).

EXAMPLE 8 Effect of Drying Temperature on Anatase Crystal Size andAdsorption Capacity

A number of samples of powdered nano-crystalline anatase product wereprepared at different drying temperatures according to the methoddescribed in Example 1 and tested for their effectiveness in removingarsenate from tap water samples. FIG. 4 illustrates the relationship ofthe drying temperature to the primary crystallite diameter of theanatase crystals in the surface-activated titanium oxide samples and tothe degree of arsenate removal demonstrated in the batch adsorptiontests. Drying the anatase product at temperatures up to 700° C. orgreater increased the primary crystallite diameter (d₀) from about 6.6nm at the lower temperatures to about 10.9 nm at the highesttemperature. The removal efficiency of the titanium oxide product towardarsenate decreased from 76% to 24% over the same temperature range.Between drying temperatures of 105° C. and about 350° C., the removalefficiency dropped substantially without a commensurate increase inprimary crystallite diameter (d₀).

EXAMPLE 9 Adsorption Capacity of a Nano-crystalline Anatase Product

An adsorption isotherm FIG. 5 was prepared to assess the adsorptioncapacity of a surface-activated crystalline titanium oxide productprepared according to the method described in Example 1, using a dryingtemperature of 105° C. The tests were performed on a sieve fraction ofthe titanium oxide product in the size range of 16-30 mesh (i.e., havingmean diameters between 0.60 and 1.18 mm). Arsenate (As (V)) solutionswere prepared in tap water at a pH of about 7 at initial concentrationsof 0-100 mg As (V)/L. The resulting isotherm indicates that theadsorption capacity of the surface-activated crystalline titanium oxideproduct is approximately 34 mg As (V)/gm of titanium oxide at thatconcentration.

EXAMPLE 10 Dynamic Capacity and Pressure Drop in a Packed Column UsingAgglomerated Surface Active Crystalline Titanium Oxide Product

Agglomerated surface active crystalline titanium oxide product wasprepared by mixing the titanium oxide product with 24 (w/w) % of a 30%(w/w) solution of ammonium-stabilized colloidal silicate solution. Whenthe mixture was dried, the agglomerated product was 5% silicate byweight. The agglomerate was screened to include 20 to 30 U.S. mesh sievesizes (595 micron to 841 micron).

A 0.45 inch diameter column was filled to a 4 inch bed depth withreferenced test media. Two additional columns having the same dimensionsas the first were filled to a 4-inch bed depth with a granular ferricoxide (trademark: AdEdge AD-33, AdEdge Technologies, Inc., Buford,Georgia, U.S.A.) and granular ferric hydroxide (GFH), (Wasserchemie GmbH& Co. KG, Osnabrück, Germany) respectively. A solution of water wasprepared as per ANSI standard 53 (“NSF 53 challenge water”) meeting thespecification at pH 8.5, as shown in Table 2:

TABLE 2 Composition of NSF 53 challenge water Parameter mg/kg, Spec SiO220 Mg 12 SO4 50 N 2.0 F 1.0 P 0.04 Ca 40 Total Chloride 0.5 As 0.05

The prepared solution was passed through the columns at 5 gallons perminute per square foot (gpm/ft²) of media surface area in the columns,equating to an EBCT of 30 seconds.

The pressure differential developed by the flowing water through thebed, and the arsenic content of the effluent water from each bed ofmedia were recorded. The arsenic content of the effluent water from theagglomerated surface activated titanium dioxide did not exceed 10 ppbuntil after approximately 8,000 bed volumes of feed water has passedthrough the column (at about 10.4 ml per bed volume), whereas the columncontaining the AdEdge E-33 had an effluent water composition containinggreater than 10 ppb arsenic at about 1,500 bed volumes of feed water,and the GFH had an effluent water composition containing greater than 10ppb arsenic at about 3,000 bed volumes of water. The pressuredifferential created by the flow of feed water through the columncontaining the agglomerated surface activated titanium dioxide did notexceed approximately 1 psi. A similar column containing agglomeratedsurface-activated titanium dioxide and operated at a flow rate of 20gpm/ft² of media surface area exhibited a pressure drop of drop of 2.25psi in the column. The pressure differential created by the flow of feedwater through the column containing AdEdge E-33 exceeded 60 psi afterapproximately 70 hours of operation. The pressure differential createdby the flow of feed water through the column containing the GFH exceeded3 psi after approximately 10 hours of operation. The agglomeratedsurface activated titanium dioxide therefore removed arsenic moreeffectively and resulted in a lower pressure drop than either of theother two materials tested.

EXAMPLE 11 Adsorption Isotherms for Surface-Activated CrystallineTitanium Oxide-Agglomerate and Granular Ferric Hydroxide Media

The performance of surface-activated titanium oxide granulate preparedas in Example 10 and granular ferric hydroxide (GFH) (Wasserchemie GmbH& Co. KG, Osnabruck, Germany) were compared by adsorption isotherms inNSF 53 Challenge Water at pH 6.5 and 8.5. As seen in Table 3, Theremoval of As(V) was greater for the surface-activated titaniumoxide-granulate than for the GFH.

TABLE 3 Adsorptive Capacities of Surface-Activated Titanium OxideGranulate and Granular Ferric Hydroxide Q (grams As(V) adsorbed Media pHper Kg media) GFH 6.5 4 Surface activated titanium oxide 6.5 12granulation GFH 8.5 5 Surface activated titanium oxide 8.5 7 granulation

EXAMPLE 12 Adsorption Isotherms for Agglomerated Surface-ActivatedCrystalline Titanium Oxide Product in NSF53 Challenge Water ContainingPhosphate

The adsorption performance of agglomerated surface-activated crystallinetitanium oxide product, prepared as in Example 11, was tested in NSF 53Challenge Water, to which sodium phosphate was added, at pH 6.5. Initialconcentrations of phosphate in the range of 0.12-12.3 ppm had no effecton the capacity of surface-activated crystalline titanium oxide product.At 10 ppb As (V) and 100 ppb As (V), the capacity of agglomeratedsurface-activated crystalline titanium oxide product was 4.6 g As (V)/Kgmedia and 9.2 g As (V)/Kg media, respectively.

EXAMPLE 13 Comparison of the Batch Adsorption of Arsenate from AqueousSolution by Nano-Crystalline Anatase and Granular Ferric Hydroxide

Batch adsorption tests were performed to compare the effectiveness of apowdered nano-crystalline anatase product, prepared according to themethod of Example 1 using a drying temperature of 105° C., and GFH,(Wasserchemie GmbH & Co. KG, Osnabrück, Germany) in removing (As(V) fromwater. The As (V) samples were prepared at a neutral pH in tap water toan initial concentration of 50 mg As (V)/L. The nano-crystalline anataseand ferric hydroxide were added to their respective water samples toconcentrations of 1.0 gm/L and suspended in the water samples by mixingfor about one hour. The results in Table 4 show that thenano-crystalline anatase sample removed substantially more of thedissolved arsenate (81.8%) than did the ferric hydroxide sample (34.0%).

TABLE 4 Comparison of As (V) Removal by Nano-Crystalline Anatase andFerric Hydroxide Nano-crystalline Ferric hydroxide anatase (1.0 g/L)(1.0 g/L) Initial concentration (mg/L) 50 50 Final concentration. (mg/L)9.1 33 Percent removal, % 81.8 34.0

EXAMPLE 14 Lead Removal by Filtration through a Porous Adsorbent Block

Porous adsorbent blocks were prepared by mixing 30% (w/w)surface-activated titanium oxide, 40% (w/w) powdered activated carbon,and 30% (w/w) polymer binder, then extruding the mixture through a die.Aqueous streams containing dissolved lead (Pb(II)) were filtered throughthe blocks on 20-minute cycles (i.e., 10 minutes on, 10 minutes off) for16 hours each day, with an 8-hour stagnation period overnight. Testswere conducted using an influent Pb(II) concentration of about 150 μg/Lat a pH of 8.5. As can be seen in Table 5, the porous adsorbent blocksreduced the concentrations of dissolved lead by over 98%.

TABLE 5 Removal of Lead by a Porous Adsorbent Block Effluent TreatedInfluent Pb(II) Conc. Effluent Pb(II) Conc. (gal) (μg/L) (μg/L) 0 140 1250 160 ND 750 140 3 1000 140 ND ND—Not detectable by analytical methodused (USEPA Method 200.8)

EXAMPLE 15 Toxic Characteristic Leaching Protocol (TCLP) Test Resultsand California Waste Extraction Test

The Toxic Characteristic Leaching Procedure (TCLP) (USEPA Method 1311,Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, EPAPublication SW-846) and the Waste Extraction Test (California Code ofRegulations, Title 22, Division 4.5, Chapter 11, Article 5, Appendix 11)were used to evaluate the leaching of arsenic from agglomeratedsurface-active titanium oxide product, prepared as in Example 10, bysubjecting product samples having arsenic adsorbed thereto to simulatedleaching conditions in the laboratory.

The measured concentrations of arsenic in each of three simulatedleachates were found to be below the regulatory levels of the respectivetests. Thus, the product samples would not be barred from land disposalon the basis of the regulatory limits for leachate.

Product samples were prepared for testing by equilibrating agglomeratedsurface-active titanium oxide product with an As (V) solution for 72hours to simulate a “worst case” breakthrough condition under dynamicperformance. To 28 grams of product sample were added 356 grams ofdeionized water and 50 mg of As (V) to give an initial solutionconcentration of 140 ppm As. The slurry was adjusted to pH=6.8 usingNaOH and then equilibrated by shaking for 72 hours. After equilibration,the concentration of As in a small amount of filtered solution wastested by ICP and found to contain 100±20 ppb As (V). The slurry was andair-dried overnight. The arsenic loading on the composite TiO₂ solidswas calculated to be 1,770 ppm As.

Toxic Characteristic Leaching Procedure (TCLP)

Extract Solution 1

Procedural details of the TCLP were followed. Twenty grams of compositetest sample were extracted for 18 hours according to the TCLP using 400grams of Extract Solution 1 (i.e., sodium acetate buffer at pH 4.9).Following extraction, the slurry was filtered. Arsenic in the filtratewas determined by inductively coupled plasma-optical emissionspectroscopy (ICP-OES) using a two point calibration consisting of theblank extract solution and blank extract solution fortified at 1 ppm As.

Extract Solution 2

Twenty grams of composite test sample were also extracted for 18 hoursaccording to the TCLP using 400 grams of Extract Solution 2 (i.e.,sodium acetate buffer at pH 2.9). Following extraction, the slurry wasfiltered. Arsenic in the filtrate was determined by inductively coupledplasma-optical emission spectroscopy (ICP-OES) using a two pointcalibration consisting of the blank extract solution and blank extractsolution fortified at 1 ppm As.

Waste Extraction Test (WET)

Procedural details of the Waste Extraction Test were followed Twentygrams of composite test sample were extracted for 48 hours at ambienttemperature according to WET using 200 mL of deoxygenated citrate bufferat pH 5.0. Following extraction, the slurry was filtered through Whatmanfilter paper #42 and 0.45 micron membrane filter. Because of the smallparticle size of the TiO₂ media, the slurry was also filtered through0.1 micron filter media. Arsenic in the filtrate was determined bygraphite furnace atomic absorption.

Results for the TCLP and WET studies are reported in Table 6. Themeasured level for arsenic in each extract was below the regulatorylevel of the respective test. Thus, no significant amount of arsenic wasleached from the agglomerated surface-active crystalline titanium oxideproduct sample under simulated leaching conditions.

TABLE 6 Leachable arsenic from agglomerated surface-active crystallinetitanium oxide product sample using TCLP and WET Tests. TCLP WET Regu-Soluble latory Threshold Limit TCLP TCLP WET Limit (1) Concentration(2)Extract #1 Extract #2 Extract (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) Arsenic5 5 0.1 0.1 1

EXAMPLE 16 Removal of Arsenic from Ethylene Glycol

To determine the actual adsorbent capacity in waste ethylene glycolengine coolant, less than 1 g of agglomerated surface activatedcrystalline titanium oxide, prepared as in Example 10 was mixed with40-50 g of waste ethylene glycol. The pH of test mixtures was adjustedbetween pH 4-9 using HNO₃ or NaOH. The mixture was allowed to reachequilibrium by gentle mixing on a rotary wheel for at least 12 hours.Upon reaching equilibrium, the filtrate was diluted 10-fold withdeionized water. Arsenic was determined by inductively coupled plasmaemission spectrometry using a Perkin-Elmer 4300DV instrument at 188.979nm and 228.812 nm.

Phosphate and borate frequently are present in ethylene glycolsolutions. Isotherm experiments were performed to determine the effectof phosphate and borate on arsenic adsorption. Stock solutions of 40mg/mL phosphate and 10 mg/mL borate solution in deionized water wereprepared from sodium dibasic phosphate and sodium borate, respectively.Pure ethylene glycol was mixed with deionized water and phosphate orborate solution to make a 50 wt. % concentration. Adequate amounts of As(III) and As (V) from 4,000 mg/L stock solution, typically 200-300 mg/Lin 50 wt. % glycol solution, were added and pH was adjusted to 7. Themixture was then shaken on a bed shaker for at least 4 hours. Uponreaching equilibrium, an aliquot of the mixture was filtered and thefiltrate was diluted 10-fold with deionized water. Arsenic in thefiltrate was determined.

Equilibrium adsorption isotherms were determined for As (III) and As (V)in an organic solution containing 50% (w/w) ethylene glycol and glycolcontaining phosphate and borate. The isotherms are shown in FIGS. 6 and7.

As a second alternative, sample acidification was studied. Assumingbasic phosphates compete with arsenite or arsenate for an adsorptionsite, the interference of phosphate can be minimized by changing themedia pH. It is likely that phosphates of higher basicity (e.g., PO₄ ³⁻,which has a higher basicity than HPO₄ ²⁻) will adsorb more strongly onthe adsorbent site. Reducing the pH will reduce the concentration ofbasic phosphate and hence may increase the adsorption of arsenic.However, at lower pH, the adsorption of arsenic may also decrease asproton competition for the site becomes more important.

The optimum pH range was determined from a pH-adsorption capacity studysummarized in FIG. 8. In these experiments, a slow rotor mixer was usedinstead of a bed shaker to avoid attrition of the adsorbent media. Anoptimum capacity of 12 mg As/g adsorbent was obtained in the 50% (w/w)waste glycol engine coolant at pH 5.

EXAMPLE 17 Preparation of an Adsorbent Granulate from Latex

The surface-activated titanium oxide in the form of nano-crystallineanatase was blended with a sodium latex (trademark: USCAR CP 620, UnionCarbide Corporation, South Charleston, W. Va.). The blended material wasallowed to air dry. The final agglomerate contained 20% latex solids.The agglomerate was screened to 20 to 40 U.S. Mesh (420 micron to 841micron). Using the method of Example 10, water was passed through theagglomerate. At 5,000 bed volumes, the resulting effluent had an arsenicconcentration of less than 10 μg/L.

EXAMPLE 18 Removal of Selenium from Aqueous Solution

The adsorption performance of agglomerated surface-activated crystallinetitanium oxide product, prepared as in Example 10 was tested in NSF 53Challenge Water at pH 7, to which selenium was added. The adsorptioncapacity at 10 ppb and 100 ppb Se (IV) was 2.1 and 5.0 g Se (IV)/Kgmedia, respectively.

It should be understood that the embodiments described herein are merelyexemplary and that a person skilled in the art may make many variationsand modifications thereto without departing from the spirit and scope ofthe present invention. All such variations and modifications, includingthose discussed above, are intended to be included within the scope ofthe invention as defined in the appended claims.

1. A method for removing dissolved contaminants from a solution,comprising the step of contacting a surface-activated titanium oxide inthe form of nano-crystalline anatase with a solution containingdissolved contaminants without irradiating the surface-activatedtitanium oxide.
 2. The method of claim 1 wherein the surface-activatedtitanium oxide is packed in a column. said method further comprising thestep of passing the solution through the surrace-activated crystallinetitanium oxide at a rate of less than about 20 gallons per minute persquare foot and a pressure drop of less than about 10 pounds per squareinch square foot of column length during said contacting step.
 3. Themethod of claim 1 wherein the surfare-activated titanium oxide, whenpacked in a column havinq a diameter of about 0.45 inches and a depth ofabout 4 inches, exhibits a pressure drop of less than about 1 psi whenwater is passed through the column at a flow rate of about 0.006 gpm. 4.The method of claim 1 wherein the solution comprises water originatingfrom a groundwater source.
 5. The method of claim 1 wherein the solutioncomprises effluent from a water-treatment unit.
 6. the method of claim 1wherein said solution is a wastewater stream from an industrial process.7. The method of claim 1 further comprising the step of washing at leastsome of the surface-activated titanium oxide before said contactingstep.
 8. A method for removing dissolved contaminants from a solution,the dissolved contaminants including one or more of aluminum. antimony,arsenic in the form of one or both of arsenic(III) and arsenic(V),barium, cadmium, cesium. chromium, cobalt, copper. gallium, goid, iron,lead. manganese. molybdenum, nickel, platinum, radium, selenium, silver.strontium, tellurium, tin tungsten, uranium, vanadium, zinc, nitrite,phosphate. sulfite. sulfide. and a low-molecular weight organic arseniccompound, the method comprising the step of contacting asurface-activated titanium oxide in the form of nano-crystalline anatasewith the solution without irradiating the surface-activated titaniumoxide, whereby the concentration of at least one of the dissolvedcontaminants in the solution is reduced.
 9. The method of claim 8wherein the dissolved contaminants include arsenic in the form of one orboth of arsenic (III) and arsenic (V) said contacting step furthercomprsing the step of removing at least 80 percent of the arsenic fromthe soluuon.
 10. The method of claim 9 where the portion of the arsenicremoved by said removing step comprises arsenic (III) and the solutioniS an aqueous feed stream having a pH in the range of about 1to about
 9. 11. The method of claim 9 wherein the solution includes one or more ofsulfate, phosphate. borate, nitrate, bicarbonate, iron. carbonate.nitrite, silicate. sulfite, chloride, bromide, and iodide.
 12. Themethod of claim 9 wherin the surface-activated titanium oxide has acapacity of about 4g of arsenic(V) per kg of surface activated titaniumoxide at a concentration of about 10ppb arsenic(V) in the solution at apH of about 6.5.
 13. The method of claim 9 wherein the surface-activatedtitanium oxide has a capacity of about 9g of arsenic(V) per kg ofsurface activated titanium oxide at a concentration of about 100ppbarsenic(V) in the solution at. a pH of about 6.5.
 14. The method ofclaim 9 wherein said contacting stan comprises the step of adsorbingarsenic in the form of one or booth of arsenic(III) and arsenic(V) tothe surface activated titanium oxide so that, after completion of saidadsorbing step, the surface-activated titanium oxide releases thearsenic to a concentration of less than 5ppm(w/w) of the arsenic in anaqueous extract prepared by the Toxic Characteristic Leaching Procedure.15. The method of claim 9 wherein said contacting step comprises thestep of adsorbing arsenic in the form of one or both of arsenic(III) andarsenic(V) to the surface-activated titantum oxrde so that, aftercompletion of said adsorbing step, the surface-activated titanium oxidereleases the arsenic to a concentration of less than 5ppm of the arsenicin an aqueous extract prepared by the Waste Extraction Test.
 16. Themethod of claim 8 wherein at least 50% (w/w) of the solution consists ofone or more organic chemicals.
 17. The method of claim 16 wherin saidorganic chemicals comprise a glycol.
 18. The method of claim 13 whereinsaid solution is at a pH of less than 6.